The present invention relates to a supercharger device for internal combustion engines, particularly for motor vehicles.
As is known, the maximum power of engines installed on motor vehicles, in particular on automobiles, considerably exceeds the power required during the normal use of the vehicle, the reserve power being used occasionally to achieve maximum acceleration, or maximum speed on level ground, the so-called top speed, or to climb the maximum slope.
In the normal use of the motor vehicle, the employed power generally does not exceed 50% of the maximum power and this reduction, obtained by choking the induction, is matched by a decrease of the specific performance of the engine with consequent high consumptions, imperfect combustion and therefore presence of polluting products in the exhaust system.
With the intention of improving the overall efficiency, the supercharging of endothermal reciprocating engines, both of the Otto-cycle type and of the Diesel-cycle type, has long been proposed, and consists of the compression to a greater-than-atmospheric pressure of all, or part of, the feed air before induction into the cylinders. Supercharging entails, as is known, an increase in mechanical efficiency, since the increase of the mechanical losses is much lower than the power increase, as well as an increase in volumetric efficiency and in actual thermal efficiency. This is followed by a considerable reduction in specific consumption, which can reach up to 45%.
Two types of supercharging are currently employed: the mechanical type and the exhaust-gas turbosupercharger type. The first type, used predominantly in small- and medium-cylinder capacity engines, draws the power required for supercharging from the driving shaft. Superchargers of the "Roots" type are used which are driven by the engine with the interposition of a multiplier and of a joint which starts the supercharger only at a preset number of rpm of the engine. In the second type of supercharging, reserved for engines with greater cylinder capacity, the supercharging power is supplied by a turbine which is driven by the exhaust gases of the engine, and drives a feed supercharger.
Both systems increase the maximum power of the engine but are substantially inactive at low rpm.
Their use therefore substantially improves the performance of the engine at medium and high rpm, but does not modify the power curve in terms of optimizing the power output with respect to the conditions of practical use of the motor vehicle.